1. Field of the Invention
The invention relates to a horizontal deflection circuit which is useful in a television receiver and a video apparatus using a cathode ray tube, and which generates a deflection current for horizontally deflecting electron beams by changing a magnetic field applied to the cathode ray tube from a horizontal deflection coil.
2. Related Art of the Invention
Recently, a display screen of a video apparatus has been increased in size, widened, and flattened, and such an apparatus itself has been thinned. This increasingly requests a horizontal deflection circuit to conduct in a highly accurate manner various corrections of deflection angles of electron beams so as to comply with an increased deflection current and image distortion which are caused by an increased deflection angle. In such an apparatus, moreover, requirements of energy saving, cost reduction, and minituarization produce large problems in that the horizontal deflection circuit is requested to consume a reduced power, to decrease the number of components, and to be integrated.
Hereinafter, a prior art horizontal deflection circuit will be described.
FIG. 21 shows the configuration of a prior art horizontal deflection circuit. In FIG. 21, 1 designates an input voltage which supplies a DC voltage to input terminals 2 and 2'. The reference numerals 2 and 2' designate the input terminals which receive the DC voltage. The reference numeral 21 designates an inductance element which is connected in series to the input terminals 2 and 2' through a switch element 22, and excitation energy is charged into and discharged from the inductance element in accordance with the closing and opening operations of the switch element 22. The reference numeral 22 designates the switch element which is controlled by a driving circuit 20 to be turned on and off, and 20 designates the driving circuit which outputs a driving pulse for controlling the closing and opening operations of the switch element 22, in synchronism with an output of a horizontal synchronizing circuit 12 with a preset duty ratio. The reference numeral 12 designates the horizontal synchronizing circuit which detects a horizontal synchronizing signal from a video signal and outputs a horizontal synchronizing pulse, and 23 designates a capacitor which is connected across the switch element 22 and cooperates with the inductance element 21 to constitute a resonance circuit. A diode 24 is connected at its cathode to the junction of the switch element 22 and the inductance element 21, and at the anode to the cathode of a diode 25. The diode 25 is connected at the cathode to the diode 24 and at the anode to the input terminal 2', and cooperates with the diode 24 which is connected in series to the diode 24, so as to bypass the excitation current of the inductance element 21 and the deflection current of a horizontal deflection coil 10. The reference numeral 26 designates a capacitor which is connected across the diode 24, 27 designates a capacitor which is connected across the diode 25, 10 designates the horizontal deflection coil which is connected across the diode 24 through a capacitor 11, and 11 designates the capacitor which cooperates with the horizontal deflection coil 10 to constitute a resonance circuit, thereby changing the deflection current of the horizontal deflection coil 10 in an S-shape pattern. The reference numeral 28 designates an inductance element. One end of the inductance element is connected to the junction of the capacitors 27 and 26, the other end to the input terminal 2' through a capacitor 29. The reference numeral 29 designates the capacitor. The voltage across the capacitor is controlled by a parabola control circuit 30. The reference numeral 30 designates the parabola control circuit which controls the voltage across the capacitor 29 so as to have a preset voltage waveform in synchronism with an output of a vertical synchronizing circuit 13, and 13 designates the vertical synchronizing circuit which detects a vertical synchronizing signal from the video signal and outputs a synchronizing pulse.
The operation of the thus configured prior art horizontal deflection circuit will be described with reference to FIG. 22.
FIG. 22 is a waveform chart illustrating the operations of various portions of the horizontal deflection circuit of FIG. 21. In the figure, IL indicates the waveform of the deflection current flowing through the horizontal deflection coil 10, VQ1 indicates the waveform of the resonance voltage applied across the switch element 22, IQ1 indicates the waveform of the current flowing through the switch element 22, IS indicates the waveform of the current flowing through the diode 24, J indicates the waveform of the output of the driving circuit 20, VS indicates the waveform of the voltage across the capacitor 27, VC indicates the waveform of the voltage across the capacitor 29, D indicates the synchronizing pulse of the horizontal synchronizing circuit, E indicates the horizontal blanking interval, and F indicates the horizontal deflection interval.
When the switch element 22 is turned off in the horizontal blanking interval E by the driving circuit 20, the excitation current of the inductance element 21 which has flown during the on period of the switch element 22 causes the resonance voltage waveform VQ1 which depends mainly on the inductance of the inductance element 21 and the capacitance of the capacitor 23, to be generated across the capacitor 23, so that the excitation current is rapidly reduced. Then, the inductance element 21 is rapidly energized in the opposite direction. With using a general expression, the resonance period T in this case can be expressed as follows: ##EQU1## The resonance period T is set so that a half of the resonance period T is within the horizontal blanking interval E. In the expression above, L is the inductance of the resonance circuit, and C is the capacitance. Similarly, the deflection current IL of the horizontal deflection coil 10 which has flown during the on period of the switch element 22 causes the resonance voltage waveform which depends on the capacitances of the capacitors 26 and 11 and the inductance of the horizontal deflection coil 10, to be generated, so that the deflection current IL of the horizontal deflection coil 10 is rapidly decreased and thereafter quickly raised in the opposite direction. In this case, since the capacitor 26 is sufficiently smaller than the capacitor 11, the most portion of the resonance voltage waveform generated in the above-mentioned resonance is applied across the capacitor 26. Furthermore, the resonance voltage waveform VS which depends of the capacitance of the capacitor 27 and the inductance of the inductance element 28 is generated across the capacitor 27, whereby the excitation current of the inductance element 28 which has been stored during the on period of the switch element 22 is rapidly reduced in the same manner as described above so that the excitation current in the opposite direction is increased. All the resonance circuits have the resonance periods calculated by (Ex. 1), and are matched so that the resonance periods substantially coincide with each other. Since the resonance voltage VQ1 appearing across the capacitor 23 is applied also to the series circuit of the capacitors 26 and 27, the addition voltage of a voltage VC26 across the capacitor 26 and the voltage VS across the capacitor 27 is equal to the resonance voltage VQ1 as follows: EQU VQ1=VC26+VS
When the resonance voltage VQ1 is reduced to be a zero voltage, the excitation current in the opposite direction of the inductance element 21 is regenerated to the input voltage 1 through the diodes 25 and 24, and the reverse excitation current is again reduced. At the same time, also the excitation current flowing through the horizontal deflection coil 10 in the opposite direction charges the capacitor 11 through the diode 24, and is again reduced. Furthermore, also the excitation current flowing through the inductance element 28 in the opposite direction is regenerated to the capacitor 29 through the diode 25, and again reduced.
When the switch element 22 is again turned on in the horizontal blanking interval E by the driving circuit 20, the excitation current in the opposite direction of the inductance element 21 is regenerated to the input voltage 1 through the switch element 22, and the reverse excitation current continues to be reduced. When all the excitation currents and the deflection current IL in the opposite direction of the inductance elements 21 and 28 and the horizontal deflection coil 10 are discharged to become zero currents, the input voltage 1 is applied through the switch element 22 to the inductance element 21 and the excitation current is supplied, so that the excitation energy is increased and accumulated. The voltage across the capacitor 11 is applied to the horizontal deflection coil 10 through the switch element 22 and the diode 25 and the deflection current is supplied, so that the excitation energy is increased and accumulated. The voltage across the capacitor 29 is applied to the inductance element 28 through the diode 24 and the switch element 22 and the excitation current is supplied, so that the excitation energy is accumulated. The excitation currents, and the deflection current continue to be increased until the horizontal deflection interval F is terminated, the horizontal blanking interval E is started and the switch element 22 is again turned off by the driving circuit 20. When the switch element 22 is turned off, the process is repeated with starting from the initial state. The driving circuit 20 continually drives the switch element 22 in synchronism with the video signal, in accordance with the horizontal synchronizing circuit 12 which detects the horizontal synchronizing signal from the video signal and outputs the horizontal synchronizing pulse. The deflection current which flows through the horizontal deflection coil 10 during the horizontal deflection interval F is set so that the deflection current waveform is caused to resonate by the horizontal deflection coil 10 and the capacitor 11. Since the deflection current generally forms an S-like shape, the correction is called the S-shape correction. The electron beams of the cathode ray tube are deflected in synchronism with the video signal by magnetic fluxes generated by the deflection current of the horizontal deflection coil 10. The S-shape deflection current IL is determined by the capacitance of the capacitor 11 and the inductance of the horizontal deflection coil 10, and its value is adjusted so as to comply with the properties of the cathode ray tube.
Next, the control operation of conducting the vertical line distortion correction by, in synchronism with the vertical deflection, changing the amplitude of the deflection current IL which flows through the horizontal deflection coil 10 will be described with reference to FIGS. 23 and 24. In FIGS. 23 and 24, the waveforms similar to those of FIG. 22 are identified by the same symbols, and their description is omitted. In FIG. 23, waveforms of various portions appearing when the voltage VC across the capacitor 29 is low are indicated by solid lines, and those appearing when the voltage VC across the capacitor 29 is high are indicated by broken lines. FIG. 24 in which the time axis is shortened shows the period of the vertical synchronization interval. In the figure, C indicates the vertical synchronizing pulse of the vertical synchronizing circuit 13, and G indicates the vertical synchronization interval of the video signal. It will be noted that, when the voltage across the capacitor 29 is controlled by the parabola control circuit 30, the amplitude of the deflection current IL of the horizontal deflection coil 10 changes in synchronism with the vertical synchronization interval. The parabola control circuit 30 is previously set by the vertical synchronizing circuit 13 which detects the vertical synchronizing signal of the video signal and outputs the vertical synchronizing pulse, so as to continually change the voltage across the capacitor 29 to become the parabolic voltage waveform VC in synchronism with the video signal. During the on period of the switch element 22, the voltage VC across the capacitor 29 is applied to the inductance element 28 through the switch element 22 and the diode 24, and the excitation current flows through the inductance element 28, so that the excitation energy is stored. When the switch element 22 is turned off and the off period starts, a resonance phenomenon occurs in the capacitor 27 and the inductance element 28, and the voltage VS across the capacitor 27 changes sinusoidally. When the voltage VC across the capacitor 29 changes, the excitation current which is stored in the inductance element 28 during the on period of the switch element 22 changes so that also the stored excitation energy changes. Consequently, also the sinusoidal voltage of the voltage VS across the capacitor 27 changes in proportion to the parabolic voltage waveform VC. During the off period of the switch element 22, at the same time, also the voltage VQ1 across the capacitor 23 resonates with the inductance element 21 to change sinusoidally, and also the voltage VC26 across the capacitor 26 resonates with the horizontal deflection coil 10 to change sinusoidally. The voltage VC26 across the capacitor 26 is the difference between the voltage VQ1 across the capacitor 23 and the voltage VS across the capacitor 27, and therefore changes in reverse proportion to the parabolic voltage waveform VC. The change of the voltage across the capacitor 26 causes the voltage applied to the horizontal deflection coil 10, to change, resulting in that also the deflection current IL of the horizontal deflection coil 10 similarly changes in reverse proportion to the parabolic voltage. This allows the deflection current IL of the horizontal deflection coil 10 which is generated during the on period of the switch element 22, to change in synchronism with the vertical deflection, whereby the so-called vertical line distortion correction is conducted.
Next, a prior art horizontal deflection circuit which is required to change the horizontal synchronizing signal in accordance with a video signal supplied to a display device or the like, or to comply with the so-called multiscan will be described.
FIG. 25 shows the configuration of the prior art horizontal deflection circuit. In FIG. 25, the same components as those of FIG. 21 are designated by the same reference numerals. Namely, 1 designates an input voltage, 2 and 2' designate input terminals, 10 designates a horizontal deflection coil, 11 designates a capacitor, 12 designates a horizontal synchronizing circuit, 13 designates a vertical synchronizing circuit, 20 designates a control circuit, 21 designates an inductance element, 22 designates a switch element, 23 designates a capacitor, 24 and 25 designate diodes, 26 and 27 designate capacitors, 28 designates an inductance element, 29 designates a capacitor, and 30 designates a parabola control circuit. These components have been described in detail in conjunction with FIG. 21, and therefore their detailed description is omitted. The reference numeral 40 designates voltage control means which is connected in series to the input terminal 2 and the inductance element 21. A control terminal of the voltage control means is connected to a voltage control circuit 46. The voltage control means converts the voltage of the input voltage 1 to a voltage of a predetermined level. The reference numeral 41 designates a capacitor which is connected to the junction of the voltage control means 40 and the inductance element 21 and also to the input terminal 2', and which smooths the voltage converted by the voltage control means 40. The reference numeral 42 designates a capacitor which is connected across the capacitor 23 through switch means 43, and which changes the capacitance of the capacitor 23 in response to the on/off operations of the switch means 43. The reference numerals 43 and 44 designate switch means the on/off operations of which are determined by the horizontal synchronizing frequency, and which sets the resonance conditions complying with the horizontal synchronizing frequency. The reference numeral 45 designates a capacitor which is connected across the capacitor 11 through the switch means 44, and which changes the capacitance of the capacitor 11 in response to the on/off operations of the switch means 44, and 46 designates the voltage control circuit which controls the voltage control means 40 so that the voltage previously set by the synchronizing pulse frequency of the horizontal synchronizing circuit 12 is obtained, thereby changing the voltage across the capacitor 41.
The operation of the thus configured horizontal deflection circuit will be described. As described in detail in conjunction with FIG. 21, the deflection current IL of the horizontal deflection coil 10 is generated by using the resonance phenomena of the inductance element 21 and the capacitor 23, the horizontal deflection coil 10, the capacitor 11 and the capacitor 26, and the inductance element 28 and the capacitor 27. The S-shape correction, and the vertical line distortion correction are conducted in the same manner also in the horizontal deflection circuit of FIG. 25. Therefore, their description is omitted. When the horizontal synchronizing frequency in the video signal changes, also the horizontal deflection interval F and the horizontal blanking interval E naturally change. In the case of using the above-mentioned resonance phenomena, therefore, also the resonance conditions must be made changeable so as to comply with the horizontal synchronizing frequency. Particularly, the resonance phenomena of the inductance element 21 and the capacitor 23, and the horizontal deflection coil 10 and the capacitor 11 which directly significantly affect the deflection current IL of the horizontal deflection coil 10 must change at least in accordance with the horizontal synchronizing frequency. The resonance frequencies must be caused to change in accordance with the horizontal synchronizing frequency, by turning on and off the switch means 43 and 44 so that the capacitors 42 and 45 are connected in parallel to or disconnected from the capacitors 23 and 11. In the case where the resonance frequencies must accurately correspond to the change of the horizontal deflecting frequency, naturally, the above-mentioned requirement is fulfilled by connecting in parallel or disconnecting a further increased number of capacitors and switches. Also the remaining resonance circuits are required to be designed so as to be changeable in a similar manner, and also the capacitors 26 and 27 must be provided with similar changing means, resulting in that many capacitors and switch means are required. This complicates the circuit. The inductances of the horizontal deflection coil 10 and the inductance element 21 cannot be changed. In order to maintain constant the deflection current IL of the horizontal deflection coil 10 irrespective of the change of the horizontal synchronizing frequency, therefore, the input voltage 1 applied to the horizontal deflection circuit must be changeable. This requires the voltage control means 40, the voltage control circuit 46, and the capacitor 41 to be added as the means for changing the input voltage. Generally, the relationship between a voltage V applied to an inductance L, a peak value IP of a current flowing through the inductance, and an application period TON is expressed by EQU IP=(V/L)TON
From the above, it will easily be understood that the input voltage must be changeable.
In another prior art example, the vertical line distortion correction is conducted by changing a voltage applied to a horizontal deflection circuit. In some cases, this is added to the control of the voltage control means 40. However, a change of the control voltage produces a problem in that the charging and discharging time of the capacitor 41 is delayed, and the following property may be impaired. Therefore, such a prior art has a reduced range of applications.
In the above-mentioned circuits of the prior art, however, since a large number of resonance phenomena are used, the inductance elements 21 and 28, and the capacitors 23, 26 and 27 are required, and the frequency is fixed. Therefore, there arise problems such as that it is difficult to minituarize the parts, that the setting adjustment conducted in view of also variations and temperature characteristics of parts are inevitably required, and that the circuit is complicated and the cost and the size are increased. Furthermore, the voltage control using the parabola control circuit 30 is necessary, the loss caused by the control of making the voltage changeable is large, and also the circuit loss is large.
In order to comply with the multiscan, the resonance capacitance is changed so that the resonance frequency changes in accordance with the horizontal synchronizing frequency. The switch means 43 and 44, and the capacitors 42 and 45 must be added as the means for realizing such a change. Moreover, as means for making the input voltage changeable, the voltage control element 40, the voltage control means 46, and the capacitor 41 must be added. Therefore, the circuit configuration is further complicated, and the loss produced in the process of changing the voltage is increased, thereby producing problems of the complicated adjustment, the increased cost, the increased size, and the increased loss due to the means for making the input voltage changeable. When the resonance frequencies are to correspond to the horizontal deflecting frequency in a further highly accurate manner, moreover, there arise many problems such as that a further increased number of capacitors and switch means must be added.